Laser-guided projectile system

ABSTRACT

A method and system is disclosed for guiding a spinning inflight projectile by determining the deviation of the projectile from an optimum trajectory along which the projectile would impact a target, and transmitting a signal to the projectile to subject the projectile to a correctional impulse acting substantially through the center of gravity of the projectile of sufficient magnitude to translate the projectile toward the optimum trajectory.

14 1 Jan. 14, 1975 LASER-GUIDED PROJECTILE SYSTEM [75] Inventor: BrianB. Dunne, La Jolla, Calif. [73 Assignee: Ship Systems, Inc., San Diego,Calif.

[22] Filed: Dec. 17, 1973 [21] Appl. No.: 424,936

Related US. Application Data [63] Continuation-impart of Ser. No.214,619, Jan. 3,

1972, abandoned.

52 US. Cl. ..244/3.13,244/3.21 51 Int. c1.,. F42 15 10, F4 2b 15/02 F42b15/00 58 Field ofSearch ..244/3.13,3.21

[56] References Cited UNITED STATES PATENTS 10/1971 Maillet 244/3.16

3,642,233 2/1972 Bezerie 1. 244/316 Primary ExaminerBenjamin A. BorcheltAssistant Examiner-Thomas H. Webb Attorney, Agent, or Firm-Fitch, lEven,Tabin & Luedeka [57] ABSTRACT A method and system is disclosed forguiding a spinning in-flight projectile by determining the deviation ofthe projectile from an optimum trajectory along which the projectilewould impact a target, and transmitting a signal to the projectile tosubject the projectile to a correctional impulse acting substantiallythrough the center of gravity of the projectile of sufficient magnitudeto translate the projectile toward the optimum trajectory.

20 Claims, 8 Drawing Figures PATENTED 1 4|975 3, 860. 199

sum 1 or 3 F I 4 INVENTOR.

H r BRIAN IB. DUNNE PATENTEDJAH 1 41975 3.860 199 SHEEI PDF 3 F 6INVENTOR.

BRIAN a. DUNNE PAIEMEM 3.860.199 saw a or. 3

LASER-GUIDED PROJECTILE SYSTEM This application is acontinuation-in-part from my copending application, Ser. No. 214,619,filed Jan. 3, 1972 now abandoned.

The present invention relates generally to guided projectile systems,and more particularly to a novel laser guided projectile system capableof guiding a spinning in-flight projectile toward an optimum trajectoryalong which the projectile would impact a target.

The use of various types of projectiles against manned and unmannedaircraft targets has a long tradition. The advent of guns with highfiring rates during World War II signalled a change in weaponeffectiveness. Guns firing projectiles of and 40 millimeter caliberbecame quite useful against all types of aircraft targets.

In recent times, however, the effectiveness of such guns against mannedaircraft, pilotless ramjet or liquidrocket-propelled aircraft hasdiminished.

This arises from three factors. First, the speed of the various aircraftis significantly higher than in World War II (namely about 650 mph vs.about 300 mph.) Second, the aircraft are sometimes pilotless, haveautomatic terminal homing systems and are of considerably heavierconstruction, thus rendering them more invulnerable to projectileimpact. Third, even with the high firing rates presently obtainable withmodern Gatling guns, the dispersion, or average angular error of astatistical sample of projectiles fired from the gun, is ordinarily toolarge in magnitude to allow sufficient hits to be scored.

This invention relates to a relatively simple, yet effective projectileor missile guidance system which is designed to reduce the dispersionerror and hence allow more hits to be scored on any target, thusproviding a more effective means for destroying such targets. Whileaircraft targets are one type against which the guidance system would beparticularly useful, ground and naval targets could also be moreeffectively attacked.

Many guidance systems have been proposed for missiles and projectiles.In the case of projectiles, most of these are useful only for largercalibers, (greater than 3 inches in diameter), whereas the optimumcalibers for the high-rate-of-fire guns are generally less than 40millimeters. Thus there is a need for a guidance system which would befeasible with both large and small calibers, and yet sufficientlycompact, light-in-weight, simple and reliable in design, and low enoughin manufacturing cost to be a practical improvement. In the followingdescription, the system is particularized to a projectile fired from agun. The invention, however, is also applicable for the guidance of aspinning rocket, or missile, and the word projectile when used in thefollowing description, should be understood to include such spinningrockets or missiles.

This invention, then, relates to a method and system for guiding aprojectile in flight so that the natural dispersion or scatter of anumber of sequentially-fired projectiles is reduced substantially, sothat more hits are registered on the target. The principal object of theinvention is to provide a sufficiently simple, small and lightweightsystem so that a reasonably small caliber, such as a 20, a 35, or a 37millimeter diameter projectile, can be effectively guided to a target bythe use of a laser beam.

It is assumed that means are provided for tracking the projectiles tothe target, such as by the use of doppler radar, or passive optical orinfrared tracking of the projectiles by the use of radiation sources inthe projectiles, which tracking system would provide the information forthe proper positioning of the guiding laser beam, by a servo-actuationdevice, so as to enable calculation of the correct lead angle for theoptimum interception of the target by the projectile or projectilestream. Such systems are in a practical state of development. Thecomputation of the trajectory of the projectile, including decelerationdue to air drag, and calculation of the target position, including leadangle, and so forth, and the determination of the optimum aimingdirection is straightforward and reduced to practice and would requireno further explanation to those reasonably skilled in this art.

Another object of the invention. is to utilize light from a narrow,rectangular or other suitably-shaped crosssectioned, collimated,circularly-sweeping laser beam to provide directional information to acompact sensing system in a projectile in such a way that sufficientguidance can be imparted to the projectile so that it will more probablyimpact with the intended target.

A further object of the device is to provide a system by the use of acircularly-sweeping, collimated laser beam with rectangular or othersuitable cross-sectional area and a computer which is programmed withthe specific ballistic data of a given projectile and measured initialvelocity of the projectiles so that optimum guidance is given to theprojectile, taking account of the statistical spread or scatter of theprojectiles about the given aim direction of the barrel or barrels ofthe firing gun system.

A still further object of the invention is to provide acountermeasure-proof guiding laser beam by the use of an intermittentmodulation or pulsation of various wavelengths within the laser beam, byeither an amplitude modulation or a coded sequence.

Such signals would be transmitted through the earth s atmosphere at theranges of interest with a high probability. Included in this informationwould be the angle of the projectile from the center of the laser beam,said angle being measured from the projected vertical in a planeperpendicular to the beam and passing through the projectile; also areference vertical by sensing the earths magnetic field intensity atboth the laser and the projectile by the use of a rotating Helmholz coilat each location.

A still further object of the invention is to provide, by means of smalloptical detectors, filters, light-sensitive cells, and a magneticintensity coil, coupled with suitable, compact, and reliable integratedor miniaturized circuitry to activate one or more discrete radialimpulses, which are produced by the acceleration of small masses,employing propellant or high explosive energies so as to provide smallchanges in velocity of the projectile in a direction normal to orperpendicular to the direction of motion of the projectile along itstrajectory or flight path.

Yet another object of the invention is to provide a projectile havingnovel impulse reaction means thereon responsive to a predeterminedsignal to effect a net impulse force on the projectile which passessubstantially through the center of gravity of the projectile.

These and other objects of the invention will become apparent to personsskilled in the arts and techniques of lasers, gunnery, rocketry, and guncontrol systems by reference to the following description when takenwith the accompanying drawings which illustrate the inventive principle.

FIG. 1 illustrates a projectile firing system in accordance with thepresent invention having a rectangular laser guidance beam scanning incircular fashion about a chosen point on an optimum trajectory forprojectile impact;

FIG. 2 is a side elevational view of one embodiment of a projectilecontaining a guidance system in accordance with the present invention,windows to accept the laser signals being shown on the boatail, andthree guidance masses being located on a plane passing through thecenter of mass of the projectile;

FIG. 3 is a diagramatic view illustrating the method of generation ofthe beam, encoding various guidance information, and development of thecircular scan of the rectangular laser beam;

FIG. 4 depicts a pair of graphs. In the graph denoted by (A), thewaveform shown is a voltage across a spinning Helmholtz coil, which cutsthe earths field lines. This coil is located in the projectile. In graph(B), the voltage across a similar coil mounted at the laser beam sourceis shown. The vertical line on each graph represents the electricalsignal when the coil is in the reference vertical position;

FIG. 5 is a 90 sectional view looking down-range toward the target. Thespinning projectiles are statistically scattered about their optimumtrajectory (at the origin of the coordinates in this figure). Theintercepted rectangular laser beam transmits to the projectilesinformation as to their individual coordinates, as well as the range tothe target and information as to true reference vertical;

FIG. 6 is a cross-sectional view of the projectile, looking down-range.A small mass is shown being explosively projected at an appropriate spinangle of the projectile causing it to translate toward the origin, whichrepresents the optimum trajectory for target impact;

FIG. 7 is a perspective view of a projectile containing a guidancesystem in accordance with another embodiment of the invention; and

FIG. 8 is a partial transverse sectional view taken substantially alongthe line 8-8 of FIG. 7.

In order to simplify the description of the system, a particularprojectile will be chosen, and a particular laser beam system, and alsoa particular number of guiding wavelengths and impulses and so forth,however, it is understood that the system may be usefully employed withother projectile calibers, lasing wavelengths, number and coding of theguiding impulses, particular geometries of the guiding laser beam, andso forth. The caliber described in the following description is 37millimeters, because such a round has sufficient size and weight toeasily accommodate the guidance system, although smaller or largerprojectiles could also be used if desired. The type of round chosen todescribe the present invention is basically a highexplosive-filledshell, with a shell-destroying tracer and a point-detonating fuze.

For a given gun aiming situation, the ballistics of the projectiles arequite accurately known, but due to the random processes, involving smalldifferences in effects of powder load, projectile shape and mass,frictional forces as the projectile leaves the gun, small differences ineffects of cloud water, small differences in frictional force due tofluctuations in wind and air density, the stream of projectiles willtend to scatter about the aim direction, such scatter being known as thedispersion of the projectiles and is an accurately measurable quantity,by the performance of a test with many rounds. It is of importance forthe proper description of the guidance system to estimate the magnitudeof this dispersion. In general, for a practical gun or missile system,it will be an angle of about 5 to 15 milliradians, by which is generallymeant that in travel along its trajectory, the projectile or missilewill tend to deviate in a statistical manner about 5 to 15 feet in every1,000 feet of travel. Thus, if a small velocity can be imparted in somesimple and accurate and reliable manner which is of magnitude 5 to 15thousandths of the instantaneous projectile velocity, the projectilecourse could be corrected.

For clarity of exposition and description, the component systems of thelaser guidance system are separately described. These are, first, thelaser guidance beam, second, the projectile laser illumination sensingsystem, and third, the projectile detonation impulse system. A specificsystem is chosen, which may or may not be optimum, in order to betterdemonstrate the workability, feasibility, and utility of the guidancemethod and hence some of its advances over the present state of the art.

With the goal of providing a useful beam with the minimum of equipment,a specially-modified argon-ion laser is employed. The laser tube 1,consists of a gas reservoir 2, connected to a precision-bore, air-cooledquartz tube 3, having an inside diameter of about 5 centimeters and alength of about centimeters. Electron flow for the unit is from a hotcathode 4, through the active lasing region to the anode 5. A bypasstube on one end of the laser tube is connected to a reservoir toequalize the gas pressure and to improve the pumping efficiency. Aground, located near the bypass tube forces the electrons to flowthrough the quartz tube. Confocal optical resonators 6, are externallymounted so that the laser light may pass through the end quartz windowwhich is mounted at the Brewsters angle 7. The voltage required to passthe current through the tube is about 12 kV and is supplied through aresistor. A coil of wire, 8, wrapped around the quartz tube 3, suppliesa continuous radio-frequency energy required to produce ionization ofthe argon gas contained within the quartz tube.

Gas pressure can be varied to effect optimization of the lasing action.Light output from such a laser is given by the following table:

TABLE 1 SPECTRAL OUTPUT OF ARGON ION LASER The power which is scatteredout of the beam-reduces the propagation power of the primary beam fromabout 0.02 decibels per kilometer to about 3 decibels per kilometer fora clear to a light-hazy atmosphere. Because of the fact that thescattering losses depend on the inverse fifth power of the wavelength,it is preferably to operate the system at wavelengths in the opticalregion rather than in the ultraviolet. Use of the near infrared regionis also possible since there are roomtemperature detectors which operatein this region. Continuous gas lasers such as those employing carbondioxide, nitrogen, helium or water vapor, which produce monochromaticlight at 10,600 A, have attenuation losses which are larger than thosefor wavelengths in the visible spectrum, but these could also beemployed. To achieve a system which is nearly impossible tocountermeasure, three or more wavelengths may be employedsimultaneously. In the case of the argon-ion laser, these might be the5145 A, 12; the 4965 A, 13; and the 4880 A, 14 lines. These are producedwith high efficiency as shown in TABLE 1.

Spectral filters 19, using interference layers can be utilized to absorbother wavelengths. The above three wavelengths would then transmit, in amanner extremely difficult to counter-measure, the various necessaryinput data to the projectile.

To effect pulse coding of the laser beam, the laser itself may be pulsedat high rates, electrically. Pulses of length between 0.4 and 3microseconds are easily produced with an argon-ion laser. The outputpower is related, in such a mode of operation, to the gas pressure andthe peak anode current.

An alternate method for producing a train of pulses, either coded oruncoded, is by the use of three or more mechanical beam choppers orsectored filter discs 9 which are rotating at various angular rates andthrough which the beam passes.

The light energy from the laser can be concentrated into a very narrowbeam 10. The angle subtended by the beam at the ranges of interest forthis device is primarily dependent upon the quality of the optics in thelaser apparatus, but also upon fluctuations in the density in theatmosphere, (refractive or bending effects), and to energy loss due tointeractions from scattering processes with small density fluctuationsor particulate matter such as dust or water droplets as the scatteringcenters. The angular width 11, of the rectangular laser beam can bequite small. For the application described here, an angle of onemilliradian would be easily obtainable.

Since the laser beam intercepts air density fluctuations orconcentrations of particulate matter suspended within the atmosphere, acertain fraction of the beam power is scattered out of the beam andlost, however the scattered intensity is in the generally forwarddirection of propagation.

As the projectile moves outward in the general direction of the target15, it will be in the circularly sweeping rectangular laser beam, thecenter of rotation of this beam being directed toward some point on theoptimum trajectory 16 to the target, as calculated by the systemcomputer 17. Some radiant energy is attenuated or scattered out of thelaser beam, as has been discussed previously. However, a sufficientfraction of the laser beam energy is intercepted and transmitted througha small window or windows 18, located, for example, on the projectileboatail. Such a window or windows may be constructed from any number ofmaterials including glasses, fuzed silica, or quartz. The opticalradiation is focused on the sensitive photodetector element 19. Thisagain could be chosen from among a wide variety of currently availablematerials. Lead selenide, or lead sulphide photoconductive cells are twodetectors which would be responsive to radiation from the argon-ionlaser, and could be used at room temperatures, not ordinarily requiringcooling. The electrical signals from such light sensitive cells are thenamplified by microcircuit amplifiers, then processed by state-ofthe-artmodular circuits 20 which may be presently obtained from many industrialsources and are easily interconnectable to produce the functionsrequired by the system. Such circuit elements are extremely lightweight,use very low electrical currents, and are extremely compact, because ofthe recent advances in this art, now including many extremely complexand very small circuits employing what is known aslargescale-integration. This is mentioned because this invention is onlypossible in practice by the use of advanced modular or othermicrocircuit techniques.

If the laser radiation is of the appropriate wavelength and modulation,and a certain pulse length as determined by the rate of spin of theprojectile and the narrowness of the rectangular beam and distance awayfrom the center of rotation of the primary axis of the laser beam, thenan electrical firing pulse is appropriately delayed and then conductedto a particular miniature detonator 21, in the guidance band 22, thedetonator being chosen so as to effect the optimum discrete change inthe radial impulse delivered to the projectile. The correctional impulseneeds to be chosen in such a way that the projectile will impact thetarget with a much improved probability. This can be done by the use ofdifferent correcting masses in the guidance band, or different amountsof explosive which propel said masses or possibly both. Because of thefact, as was pointed out earlier, that the laser radiation is mainly atsmall angles to the direction of the optimum trajectory, it isadvantageous for the small window or windows of the guidance system inthe projectile to accept radiation from the direction opposite to thedirection in which the projectile is moving. Such a window or windowscould be easily mounted on the rear end or boatail of the projectile.

In the following, consideration is given of how this guidance might beeffected in practice. It is assumed that the guidance system isinstalled into a 37 millimeter projectile 23. A typical velocity of thisprojectile is 3,000 feet per second. It is assumed in this analysis thatthe target is fixed at a range of 2,000 feet. The projectile will takeapproximately 0.66 seconds to reach the target if the latter is fixedand the gun will have to be elevated about 4 mils, if the target and gunare approximately at the same elevation, to compensate for the effect ofgravity during the projectile flight. As shown in FIG. 1, the laser beamwill be directed at an appropriate angle so that at or near the midpointof the projectile flight 24, for example, any corrections in azimuth orelevation angle can be applied to the projectile by the discrete radialimpulse system to bring it more nearly onto the optimum trajectory.

In order to determine the radial distance of the projectile away fromthe optimum trajectory at the half range position, the laser beam, ofrectangular cross section 25, in a plane perpendicular to the directionof the propagating light beam, is rotated at a frequency f,,. This canbe accomplished simply in practice by passing the beam through anaperture 27 to render it rectangular in shape, then through a deviceknown as a beam expander, if necessary, to increase the long dimensionof the rectangle, and then through a rotating dove prism 28, orequivalent mirror array, which will rotate the whole rectangular beamabout the center of rotation 26, which, for the example chosen, isplaced on the trajectory midpoint. (FIG. 1)

The small window or windows located on the boatail of the projectileintercept and filter the various wavelengths providing signals to thevarious amplifier channels and microcircuit decision elements within theprojectile. e

The pulse length of the green line at 5145 A depends upon the frequencyof rotation of the dove prism f 28, the width of the scanning rectangle,11, and the radial distance from the point of optimum trajectory, r.

In order to effect a small correctional velocity small masses 30, areejected radially from the projectile at an appropriate time. Because ofthe requirements of small space, weight, complexity and fabricationcost, only a limited number of correcting impulses are given to theprojectile.

Let us assume, for the purposes of this description that there are threemasses, perhaps made of steel or brass, and accelerated by small amountsof propellant or high explosive 31. Explosive weights of perhaps twiceto three times the weights of the guidance masses would be appropriate.The explosive might be a secondary type initiated by a microdetonatorwhich may have a wide variety of component explosive compounds, such aslead styphenate, as a primary explosive, followed by a train of a moresensitive booster explosive material, such as tetryl, followed in turnby the secondary explosive, such as HMX, RDX, or PETN. The secondaryexplosive is generally quite brisant, and for this reason a thin layerof a buffer material, such as a soft plastic, would ordinarily beinterposed between said secondary explosive and the guidance mass, toinsure smooth and reproducible acceleration of the latter. However, itis important to note that the guidance mass is accelerated and out ofcontact with the projectile in a very short time interval, 2microseconds or less being typical, and in this time the projectilewould only rotate around its spin axis about 1 in angle. The detonationof the guidance mass accelerating explosive would produce some shockeffect in the body of the projectile. If the high explosive fill of theprojectile is proximate to the guidance mass, a thin layer ofshockabsorbing material, such as rubber, or a plastic, such aspolyethylene, can be interposed between the explosive fill and the metalprojectile body to prevent shock waves of any appreciable magnitude fromintercepting said explosive fill.

A simplified way of considering the correcting impulse required iscontained in the following simple analysis. It is first assumed that thedispersion of the projectile is denoted by r. The radial velocity of theprojectile away from the optimum trajectory (Av) can then be related tothe projectile velocity, (v) through the following relation:

Avlv=r Typical projectile velocities at the target would beapproximately 2,500 feet per second. The velocity at which the smallguidance masses can be projected, v,,, by the use of a microdetonatorand a small high explosive charge is in the neighborhood of 5,000 feetper second. The following equation gives the guidance mass, m,,, toeffect the required correction to a projectile of mass m.

2Avm v m,,

The guidance mass, m,,, can be calculated from the above equation andEquation 1.

As was previously pointed out, in typical practice, the guidance massspeed will be approximately twice the projectile speed. Thus Since thevalue of the total dispersion r is about 7 X 10 while in isapproximately 600 gm, thus m, 4.2 gm.

This mass is an acceptably small fraction of the total projectile massand hence will not deteriorate the terminal fragmentation or penetrationeffectiveness of the round.

The projectile is spinning in free flight at a rate determined by thetwist of the rifling. For example, with a rifling twist of l in 17calibers, the spin rate would initially be approximately 1,430 rps, orabout 1.4 revolutions for every millisecond of flight. For a velocity of3,000 feet per second, this yields a single revolution for each 2 feetof projectile travel along the trajectory.

If the axis of a spinning mass is rotated in a direction normal to theaxis, the mass will suffer a gyroscopic precession, by which isgenerally meant that the spin axis tends to rotate in a directionperpendicular to the direction of the applied force. Likewise, if theprojectile is rendered an impulse at a position off the plane 32 normalto the axis and passing through the center of mass of the projectile,the axis of the projectile will undergo precession; it will describe acone, and the resulting aerodynamic forces on the projectile will causeit to yaw or stray off course in an uncontrolled manner. Thus, one ofthe essential features of this invention is the location of the guidancemasses on a guidance band which is at or very near a plane perpendicularto the projectile axis and which passes through the projectile center ofmass 33. Depending upon the projectile flight time to the target, aradial impulse would be chosen which would optimize the probability ofinterception with the target. Thus, the radial correction impulseapplied, for a given error in distance 34, from the predictedtrajectory, might be small at the initial segments of the trajectory,but then increase as the time interval to correct the course growsshorter, with decreasing distance to the target. For this purpose, amicrocircuit computational element is employed; this circuitry beingpowered, for example, by a small electric generator taking its powerfrom the spin-up of the projectile during acceleration in the barrel, ora lightweight, compact battery 35, activated by setback forces duringprojectile acceleration in the gun barrel, as is commonly practiced inproximity or VT fuzes.

The angle qb (FIG. is communicated to the projectile sensing system byan amplitude-modulated signal superimposed on the argon-ion laser greenline at 5,145 A, the modulation having, for simplicity, a frequencyrelation to the angle 4) of direction, a proportionality as follows:

The projection of the true vertical 36, can be established within theprojectile a follows: A dielectric material in the side of theprojectile in the form of a small cylindrical plug, carries embeddedwithin it a small Helmholtz coil 37. As the projectile spins, a voltageis developed across the terminals of this coil, said voltage dependingon the direction of the intercepted magnetic lines of the earths field38. Since the intensity of this field is generally about 0.2 gauss, thevoltage developed by the coil is sufficient for the operation of thissensor. A typical voltage waveform across the coil as a function ofangle of rotation is shown in FIG. 4A. Because the earths field variesin dip, or vertical angle, and declination, or horizontal angle, theangle at which the magnetic field maximum occurs from the projectedvertical will vary. This angle is shown as =0 in FIG. 4.

At the laser, another Helmholtz coil 39 is located, with its geometryand rotational axis nearly coaxial with the projectilemagnetic-field-sensing Helmholtz coil. Thus the two voltage signals willbe similar in waveform to one another irrespective of the direction ofaim of the gun and the guiding laser beam. However, at the laser, areference projection of the true vertical is readily available; a simpledamped pendulum would provide, with sufficient accuracy, 21 referenceprojected vertical. This data could also be provided from fire controlsystems.

The voltage signal at the laser magnetic sensing system is shown in FIG.4B. It may have a different amplitude and frequency, but the ratio H,,,,the maximum value, to the value at the vertical plane H will be nearlythe same as that on the projectile. This may be written as follows:

7 H,, H, (Projectile) H,,, H, (Laser) Thus, the signal amplitude at theprojectile which represents the projection of the true vertical can beeasily determined. Hence the angle a 1. is also determined.

The variable 'y can then be transmitted to the projectile by the laserbeam employing an amplitudemodulated signal of frequency f on the blue(4,880 A) line.

Normally, the earths magnetic inclination will be between useful limitsand the magnetic field strength (about 0.2 gauss) will be sufficient sothat the projectile vertical-sensing system will be simple, accurate,reliable, and nearly impossible to countermeasure by the enemy.

The spinning Helmholtz coil on the projectile also supplies pulses to amicrocircuit counter 40 which totals the number of projectilerevolutions to a given range. Thus, knowing the number of revolutions,the initial projectile velocity, and the rate of decrease of the spinrate, due to frictional forces in the air, allows the range to bedetermined with excellent precision.

Amplitude-modulated signals of frequency f;, can be sent down the laserbeam on the 4,965 A blue-green line to specify the range at which thecorrection impulse should be initiated. For purposes of illustration, wespecify here that this correction would begin at midrange, or halfway tothe target, which is at range R.

fa s R The angle L is known by the design of the projectile. Since theangle a L is known from the projected vertical sensing Helmholtz coil inthe projectile, with the normalizing signal sent down the laser beam bythe modulation of the 4,880 A line. When the angle a is nearly equal tothe angle the detonator on an appropriate guidance mass is fired,projecting this mass out at an angle (1) thus imparting to theprojectile a correcting impulse toward the optimum trajectory (at thecoordinate origin in FIG. 6).

Appropriate logic or computational elements in the subminiaturizedcomputing circuitry would select the optimum discrete impulse, of thethree available to effectuate the optimum trajectory correction, whichwould depend upon the following factors: the range from the gun, asdetermined by the magnetic field spin counter of the projectile, whichinitiates action upon firing setback or acceleration; the distance errorfrom the correct trajectory, determined by f, and the time that thescanning rectangular laser beam intercepts the projectile.

Various components of this system can also be utilized in afurther-developed system to provide improved fuze function. For example,many of the components of an active infrared or visible light proximity'fuze are already included in the system, such as windows, detectors,detector circuitry, filters, power supplies, and so forth. Also, updatedrange data is available within the projectile with this system, so theprojectile can be detonated at this range to substantially increase thedamage radius.

FIGS. 7 and 8 illustrate another embodiment of a projectile, indicatedgenerally at 40, which may comprise a rocket or missile constructed inaccordance with the present invention. The projectile 40 differs fromthe projectile illustrated in FIG. 2 primarily in its impulse reactionmeans for establishing a net impulse force to effect lateral movement ofthe projectile toward a desired trajectory in response to apredetermined signal applied to the projiectile. The peripheralconfiguration of the projectile 40 is generally similar to theperipheral configuration of the projectile illustrated in FIG. 2. Theprojectile 40 includes an intermediate section having an annulargenerally cylindrically shaped peripheral wall 41 which overlies a longgroove 42 formed in a cylindrical housing portion 43 of the projectilebody. The long groove: 42 may take the form of a plurality of U-shapedgrooves which are connected in end-to-end relation such that the ends ofthe legs of each U-shaped groove are each connected to one end of anadjacent U-shaped groove to form a long groove disposed peripherallyabout the housing 43. The long groove 42 is positioned such that a planeintersecting the groove 42 at the midpoint of each longitudinal legportion of the groove and disposed perpendicular to the longitudinalaxis of the projectile 40 passes through the center of mass of theprojectile 40, the long groove being connected to a microdetonator by anexplosive train.

The groove 42 in the projectile 40 contains a high explosive materialwhich completely fills the groove 42. The high explosive material maycomprise a secondary type explosive capable of being initiated by amicrodetonator and may have a wide variety of components of explosivecompounds, such as lead styphenate, as a primary explosive, followed bya train of more sensitive explosives such as tetryl, followed in turn bythe secondary explosive, such as I-IMX, RDX, or PETN. The explosivematerial may be bound together by various binding materials to effect anoptimum detonation speed by variance of the density of the bindermaterial. The high explosive, if bound in a form initially having lowviscosity, can be then easily injected into the long groove, laterhardening into a more rigid consistency. The high explosive materialdisposed within the groove 42 is capable of high order detonation and,upon being selectively detonated with respect to the angular position ofthe point of detonation relative to vertical, will effect a very rapidrate of detonation along the length of the groove. An explosive materialis selected having a rate of detonation, considered along the length ofthe groove 42, which will maintain the point of detonation in a fixedangular position relative to a true vertical even though the projectileis spinning about its longitudinal axis at a relatively high rotationalspeed. In this manner, when the high explosive material within thegroove 42 is detonated, a high order detonation will be effected whichwill act against the inner surface of the annular peripheral wall 41accelerating it so as to effect a net impulse force acting perpendicularto the longitudinal axis of the missile 40. The materials which surroundthe groove may be of a friable nature so that after detonation theresulting underlying surface is smooth, thus, reducing the air dragforces due.to projectile spin. The rate of detonation of the highexplosive material within the groove 42 and the balanced geometry of thegroove 42 relative to the center of mass of the projectile 40 are suchthat the impulse force created by detonation of the explosive materialwill create an average net impulse force which acts through the centerof mass of the projectile 40 in a chosen direction perpendicular to thelongitudinal axis of the projectile.

As an alternative to employment of small windows on the projectileboatail, as employed in the projectile illustrated in FIG. 2, theprojectile 40 may employ a pair of laser light sensor elements 44 whichare positioned within an axial recess or opening 45 in the base portionof the projectile 40. The recess 45 may be covered with a thin coverplate when the projectile is being accelerated in the gun barrel so asto protect the sensor elements 44 from the high temperature propellantgases and smoke which could cause obscuration, this cover plate beingdropped off in flight after the projectile exits from the gun barrel.The laser light sensor elements 44 serve to transmit optical radiationfrom the laser guidance beam to a photodetector element (not shown)housed within the projectile 40, such photodetector element beingsimilar to the above referenced photodetector element 19 mounted withinthe projectile illustrated in FIG. 2. As an alternative to the use ofthe earths magnetic field as a method for determining the true verticalof a fiducial point on the projectile, as is illustrated in FIGS. 4 and6, the center of the angle of acceptance of the laser light sensorelements 44 may be canted at various angles to the longitudinal axis ofthe projectile so that they accept light from the guiding laser beamonly at a certain rotational angle, thus providing a vertical electricalreference pulse, since the longitudinal axis of the projectile on itsballistic trajectory is always at a slight angle to the direction of theguiding laser beam, as is shown in FIG. 1.

The projectile 40 includes guidance microcircuitry which may be housedwithin a suitable encasement housing 46 carried within the recess 45 inthe tail end of the projectile 40. The guidance micro-circuitry withinthe encasement housing 46 is similar to the above referenced modularcircuits 20 described with respect to the projectile illustrated in FIG.2. In other respects, the projectile 40 is guided in identical fashionto the guidance of the projectile illustrated in FIG. 2, the net impulsereaction force being effected to cause a lateral translation of theprojectile 40 from an actual trajectory toward a theoretical trajectorywhich would cause impact with a selected target.

Various other modifications may be made in the disclosed method andapparatus without departing from the spirit and scope of the invention.

Various features of the invention are set forth in the following claims.

What is claimed is:

l. A method for guiding a spinning projectile or the like having atleast one discrete mass releasably mounted in the projectile with thecenter of gravity of said mass located in a plane substantially normalto the axis of the projectile and passing proximate to the center ofgravity of the projectile, said method comprising the steps of;determining the deviation of the projectile from an optimum trajectoryalong which the projectile would impact a target, transmitting apredetermined signal to said projectile, receiving said signal by saidprojectile, and releasing at least one of said masses from saidprojectile in response to receipt of said predetermined signal by saidprojectile in a manner to impart a correctional momentum to saidprojectile sufficient to translate said projectile toward said optimumtrajectory.

2. The method as defined in claim 1 wherein said projectile includeschemical propellant means cooperative with said discrete masses toeffect release of said masses from said projectile upon selectivedetonation of said chemical propellant means, and wherein saidpredetermined signal to said projectile is transmitted and received in amanner to selectively detonate a propellant means and release at leastone of said discrete masses to impart said correctional momentum to saidprojectile.

3. The method as defined in claim 1 wherein said correctional momentumapplied to said projectile is imparted in a radial direction relative tothe axis of said projectile.

4. The method of claim 2 wherein said chemical propellant meanscomprises high explosive means cooperative with said masses toselectively release at least one of said masses from said projectileupon selective detonation of said explosive means, and wherein said stepof transmitting said predetermined signal to said projectile andreceiving said signal by said projectile are sequenced in a manner toeffect said selective detonation and release at least one of said massesto impart said correctional momentum to said projectile.

5. A method for making an in-flight correction of the trajectory of aspinning projectile, comprising the steps of selectively subjecting theprojectile to a correctional impulse essentially at a right angle to theaxis of the missile and passing adjacent the center of gravity of themissile, said impulse being created by a detonation of sufficientmagnitude and direction to change the trajectory traveled by theprojectile at the time of impulse to a desired trajectory thereby tosubstantially improve the probability of the projectile hitting apredetermined target.

6. The method as defined in claim wherein said projectile has highexplosive impulse reaction means thereon, and wherein said correctionalimpulse is created by selectively detonating said high explosive impulsereaction means.

7. A method for guiding a spinning projectile to a target, saidprojectile having at least one discrete guidance mass mounted thereonwith the center of gravity of said guidance masses located substantiallyin a plane normal to the projectile axis and passing substantiallythrough the center of gravity of the projectile, said discrete massesbeing adapted to be accelerated outwardly from said projectile in agenerally radial direction to provide a correctional momentum to thespinning projectile and translate it laterally into an optimumtrajectory so that the probability of impact with a chosen target isimproved, said method comprising the steps of transmitting to saidprojectile a signal representative of the angular position of apredetermined surface point on said projectile relative to a projectedvertical, transmitting to said projectile a signal representative of theinstantaneous angle of the projectile relative to said pro jectedvertical, transmitting to said projectile a signal representative of thedistance of the projectile from an optimum trajectory path, transmittingto said projectile asignal representative of the distance that theprojectile is along its trajectory path, receiving said transmittedsignals by said projectile and effecting release of at least one of saidguidance masses from said projectile in response to receipt of saidsignals, thereby effecting lateral translation of said projectile in amanner to establish a trajectory which increases the probability ofimpact of the projectile with the intended target.

8. The method as defined in claim 7 wherein said projectile includes aplurality of discrete guidance masses, and repeating the sequence ofsteps as required to maintain the desired trajectory of said projectile.

9. A missile guidance system for guiding a spinning impulse reaction bysaid impulse reaction means in a manner to impart a correctionalmomentum to said projectile and cause said projectile to translatetoward said optimum trajectory.

10. A system as defined in claim 9 wherein said impulse reaction meansincludes one or more discrete masses releasably mounted in saidprojectile, and high explosive means cooperative with said discretemasses to effect release of said masses from said projectile uponselected detonation of said high explosive means, and wherein saidpredetermined signal is effective to selectively detonate said highexplosive means and effect release of at least one of said discretemasses.

11. A system for guiding and reducing the aim dispersion ofa spinningprojectile or the like to a target, comprising, in combination, at leastone small discrete guidance mass mounted on the projectile with thecenter of gravity of said guidance mass located substantially in a planenormal to the projectile axis and passing through the center of gravityof the projectile, each of said guidance masses being capable of beingaccelerated outwardly in a generally radial direction to provide acorrectional momentum to the projectile and bring it into a more optimumtrajectory so that the probability of impact with a chosen target isimproved, computer means contained within the projectile and capable ofreceiving input data signals transmitted to the projectile, laser beammeans capable of transmitting input signals from a source to theprojectile, means for transmitting to said projectile along said laserbeam means a signal representative of the vector from the optimumtrajectory point to the projectile, measured in a plane perpendicular tothe direction of propagation of the laser beam, means for transmittingto said projectile along said laser beam means a signal representativeof the direction of the true vertical, means for transmitting to saidprojectile along said laser beam means a signal representative of thedistance that the projectile is along its trajectory, said computermeans being operable to effect acceleration of at least one of saidguidance masses outwardly from the projectile in response to re ceipt ofsaid signals to impart a correctional impulse momentum to the projectilesufficient to bring it into a trajectory which increases the probabilityof impact of the projectile with a predetermined target.

12. A missile guidance system as defined in claim 9 wherein said meansin said projectile responsive to receipt of said predetermined signalincludes microcircuit computational element means disposed within saidprojectile.

13. A projectile for use in a system operative to guide a projectilebetween a guidance laser source and a predetermined target substantiallyalong an optimum trajectory, said projectile having impulse reactionmeans mounted thereon including means capable of being detonated in amanner to effect a net impulse force on the projectile which actssubstantially in a plane normal to the projectile axis and passesthrough the center of gravity of the projectile, and means cooperativewith said impulse reaction means and responsive to a predeterminedsignal to effect detonation of said detonation means to provide acorrectional momentum to the projectile to birng it into a trajectorywhich will increase the probability of impact of the projectile with thepredetermined target.

14. A projectile as defined in claim 13 wherein said impulse reactionmeans includes at least one discrete guidance mass releasably mounted insaid projectile substantially in a plane normal to the axis of theprojectile and passing substantially through the center of gravitythereof, said detonation means being capable of effecting release of atleast one of said masses from said projectile to provide saidcorrectional momentum.

15. A projectile as defined in claim 14 wherein said detonation meansincludes high explosive means selectively detonatable to effect releaseof at least one of said discrete masses.

16. A projectile as defined in claim 14 wherein each of said discretemasses is selectively releasable outwardly' relative to the center ofgravity of said projectile to effect an impulse momentum force whichacts in a corrective manner to provide said momentum to said projectile.

17. A projectile as defined in claim 13 wherein said impulse reactionmeans includes a long groove formed in a housing portion of saidprojectile, and high explosive means disposed within said long grooveand capable of being detonated in a manner to establish a net dicular tothe longitudinal axis of the projectile and passing through the centerof gravity thereof, said high explosive means including a high explosivematerial capable of high order detonation upon selective detonationthereof.

l9.'A projectile as defined in claim 17 wherein said 7 r projectileincludes a plurality of said long grooves, the explosive containedtherein being detonable in a sequence of steps as required to maintainthe desired trajectory of said projectile.

20. A projectile as defined in claim 17 including an annular generallycylindrically shaped wall overlying said long groove.

UNITED STATES PATENT oTTtcE CERTIFICATE @F CQEC'HN PATENT NO. 3,860,199

DATED January 14, 1975 |NVENTOR(S) Brian B. Dunne it is certified thaterror appears in the above-identified patent and that said LettersPatent are hereby corrected as shown below:

Column 2, line 48 "Helmholz" should be -=-Helmholtz Column 5, lines 4-5"preferably" should be --=preferable Column 9, line 16 "a follows"should be -as follows-- Column 9, line 54 "the angle or 1" should be -orq5- Column 10, line 20 1" should be -6 Column 10, line 21' 1" should be6-- Column 14, line 64 "biring" should be -bringfiigncd and catcd thistwenty-ninth of July 1975 [SEAL] Arrest:

RUTH C. MASON C. MARSHALL DANN Arrosling Officer (ummissiuncr nj'larenrsand Trademark-x UNITED STATES PATENT QFFICE CERTIFICATE @F PATENT NO.3,860,199

DATED January 14, 1975 INVENTOR(S) Brian B. Dunne It is certified thaterror appears in the above-identified patent and that said LettersPatent are hereby corrected as shown below:

Column 2, line 48 "Helmholz" should be --Helmholtz Column 5, lines 4-5"preferably" should be -preferable Column 9, line 16 "a follows" shouldbe as follows-- Column 9, line 54 "the angle or 1" should be --or Column10, line 20 "1" should be 6-- Column 10, line 21 "1" should be 6- Column14, line 64 "biring" should be -bring fir'gned and salad thistwenty-ninth Of July 1975 [SEAL] Arrest:

RUTH C. MASON C. MARSHALL DANN Arresting Officer (nmmissr'unvr 01'Parents and Trademark-x

1. A method for guiding a spinning projectile or the like having atleast one discrete mass releasably mounted in the projectile with thecenter of gravity of said mass located in a plane substantially normalto the axis of the projectile and passing proximate to the center ofgravity of the projectile, said method comprising the steps of;determining the deviation of the projectile from an optimum trajectoryalong which the projectile would impact a target, transmitting apredetermined signal to said projectile, receiving said signal by saidprojectile, and releasing at least one of said masses from saidprojectile in response to receipt of said predetermined signal by saidprojectile in a manner to impart a correctional momentum to saidprojectile sufficient to translate said projectile toward said optimumtrajectory.
 2. The method as defined in claim 1 wherein said projectileincludes chemical propellant means cooperative with said discrete massesto effect release of said masses from said projectile upon selectivedetonation of said chemical propellant means, and wherein saidpredetermined signal to said projectile is transmitted and received in amanner to selectively detonate a propellant means and release at leastone of said discrete masses to impart said correctional momentum to saidprojectile.
 3. The method as defined in claim 1 wherein saidcorrectional momentum applied to said projectile is imparted in a radialdirection relative to the axis of said projectile.
 4. The method ofclaim 2 wherein said chemical propellant means comprises high explosivemeans cooperative with said masses to selectively release at least oneof said masses from said projectile upon selective detonation of saidexplosive means, and wherein said step of transmitting saidpredetermined signal to said projectile and receiving said signal bysaid projectile are sequenced in a manner to effect said selectivedetonation and release at least one of said masses to impart saidcorrectional momentum to said projectile.
 5. A method for making anin-flight correction of the trajectory of a spinning projectile,comprising the steps of selectively subjecting the projectile to acorrectional impulse essentially at a right angle to the axis of themissile and passing adjacent the center of gravity of the missile, saidimpulse being created by a detonation of sufficient magnitude anddirection to change the trajectory traveled by the projectile at thetime of impulse to a desired trajectory thereby to substantially improvethe probability of the projectile hitting a predetermined target.
 6. Themethod as defined in claim 5 wherein said projectile has high explosiveimpulse reaction means thereon, and wherein said correctional impulse iscreated by selectively detonating said high explosive impulse reactionmeans.
 7. A method for guiding a spinning projectile to a target, saidprojectile having at least one discrete guidance mass mounted thereonwith the center of gravity of said guidance masses located substantiallyin a plane normal to the projectile axis and passing substantiallythrough the center of gravity of the projectile, said discrete massesbeing adapted to be accelerated outwardly from said projectile in agenerally radial direction to provide a correctional momentum to thespinning projectile and translate it laterally into an optimumtrajectory so that the probability of impact with a chosen target isimproved, said method comprising the steps of transmitting to saidprojectile a signal representative of the angular position of apredetermined surface point on said projectile relative to a projectedvertical, transmitting to said projectile a signal representative of theinstantaneous angle of the projectile relative to said projectedvertical, transmitting to said projectile a signal representative of thedistance of the projectile from an optimum trajectory path, transmittingto said projeCtile a signal representative of the distance that theprojectile is along its trajectory path, receiving said transmittedsignals by said projectile and effecting release of at least one of saidguidance masses from said projectile in response to receipt of saidsignals, thereby effecting lateral translation of said projectile in amanner to establish a trajectory which increases the probability ofimpact of the projectile with the intended target.
 8. The method asdefined in claim 7 wherein said projectile includes a plurality ofdiscrete guidance masses, and repeating the sequence of steps asrequired to maintain the desired trajectory of said projectile.
 9. Amissile guidance system for guiding a spinning projectile or the likehaving impulse reaction means mounted in the projectile with the centerof gravity of said impulse reaction means located in a planesubstantially normal to the axis of the projectile, said systemincluding laser beam means for transmitting a predetermined signal tosaid projectile, said projectile having means therein responsive toreceipt of said predetermined signal for determining the deviation ofthe projectile from an optimum trajectory along which the projectilewould impact a target and for effecting an impulse reaction by saidimpulse reaction means in a manner to impart a correctional momentum tosaid projectile and cause said projectile to translate toward saidoptimum trajectory.
 10. A system as defined in claim 9 wherein saidimpulse reaction means includes one or more discrete masses releasablymounted in said projectile, and high explosive means cooperative withsaid discrete masses to effect release of said masses from saidprojectile upon selected detonation of said high explosive means, andwherein said predetermined signal is effective to selectively detonatesaid high explosive means and effect release of at least one of saiddiscrete masses.
 11. A system for guiding and reducing the aimdispersion of a spinning projectile or the like to a target, comprising,in combination, at least one small discrete guidance mass mounted on theprojectile with the center of gravity of said guidance mass locatedsubstantially in a plane normal to the projectile axis and passingthrough the center of gravity of the projectile, each of said guidancemasses being capable of being accelerated outwardly in a generallyradial direction to provide a correctional momentum to the projectileand bring it into a more optimum trajectory so that the probability ofimpact with a chosen target is improved, computer means contained withinthe projectile and capable of receiving input data signals transmittedto the projectile, laser beam means capable of transmitting inputsignals from a source to the projectile, means for transmitting to saidprojectile along said laser beam means a signal representative of thevector from the optimum trajectory point to the projectile, measured ina plane perpendicular to the direction of propagation of the laser beam,means for transmitting to said projectile along said laser beam means asignal representative of the direction of the true vertical, means fortransmitting to said projectile along said laser beam means a signalrepresentative of the distance that the projectile is along itstrajectory, said computer means being operable to effect acceleration ofat least one of said guidance masses outwardly from the projectile inresponse to receipt of said signals to impart a correctional impulsemomentum to the projectile sufficient to bring it into a trajectorywhich increases the probability of impact of the projectile with apredetermined target.
 12. A missile guidance system as defined in claim9 wherein said means in said projectile responsive to receipt of saidpredetermined signal includes microcircuit computational element meansdisposed within said projectile.
 13. A projectile for use in a systemoperative to guide a projectile between a guidance laser source and apredetermined target substantIally along an optimum trajectory, saidprojectile having impulse reaction means mounted thereon including meanscapable of being detonated in a manner to effect a net impulse force onthe projectile which acts substantially in a plane normal to theprojectile axis and passes through the center of gravity of theprojectile, and means cooperative with said impulse reaction means andresponsive to a predetermined signal to effect detonation of saiddetonation means to provide a correctional momentum to the projectile tobirng it into a trajectory which will increase the probability of impactof the projectile with the predetermined target.
 14. A projectile asdefined in claim 13 wherein said impulse reaction means includes atleast one discrete guidance mass releasably mounted in said projectilesubstantially in a plane normal to the axis of the projectile andpassing substantially through the center of gravity thereof, saiddetonation means being capable of effecting release of at least one ofsaid masses from said projectile to provide said correctional momentum.15. A projectile as defined in claim 14 wherein said detonation meansincludes high explosive means selectively detonatable to effect releaseof at least one of said discrete masses.
 16. A projectile as defined inclaim 14 wherein each of said discrete masses is selectively releasableoutwardly relative to the center of gravity of said projectile to effectan impulse momentum force which acts in a corrective manner to providesaid momentum to said projectile.
 17. A projectile as defined in claim13 wherein said impulse reaction means includes a long groove formed ina housing portion of said projectile, and high explosive means disposedwithin said long groove and capable of being detonated in a manner toestablish a net impulse force on the projectile which acts substantiallyin a plane perpendicular to the longitudinal axis of the projectile andpasses substantially through the center of gravity of the projectile.18. A projectile as defined in claim 17 wherein said long groove extendsabout the periphery of said projectile housing and is balanced relativeto a plane perpendicular to the longitudinal axis of the projectile andpassing through the center of gravity thereof, said high explosive meansincluding a high explosive material capable of high order detonationupon selective detonation thereof.
 19. A projectile as defined in claim17 wherein said projectile includes a plurality of said long grooves,the explosive contained therein being detonable in a sequence of stepsas required to maintain the desired trajectory of said projectile.
 20. Aprojectile as defined in claim 17 including an annular generallycylindrically shaped wall overlying said long groove.